Web Site Rules for HTTP Response Headers

We have followed the Admin Help in order to set an expired date for images, but the following does not seem to work:

First we created the “Global Web Settings” document (with * for “Domino servers that host this site:”), and then a Web Site Rule:

Description: Image cache

Type of rule: HTTP response headers

Incoming URL pattern: .gif

HTTP response codes: 200, 206, 304

Expires header: Always add header (override application’s header)

Specify as date

Expires after 2018-03-28

Finally, for the server document, we enabled “Load Internet configurations from Server\Internet Sites documents”.

Any idea of what is wrong?

By the way, let us recommend the book “High Performance Web Sites” by Steve Souders.